Several months ago I purchased an iPod nano (former version) and all of a sudden today it just hung. I have no indication what caused it. Luckily a collegue of mine had the same problem about a year ago with his iPod (classic). The resolution, which also worked out for me to my satisfaction, is to follow this procedure:

• Lock the iPod (Hold button on top)
• Unlock the iPod
• Simultaneous press the Menu and center button for about 5-10 seconds
• The iPod reboots

Grz, Kris.